glMap1 and glMap2
define evaluators. glGetMap returns evaluator parameters. target chooses
a map, query selects a specific parameter, and v points to storage where
the values will be returned.

The acceptable values for the target parameter
are described in the glMap1 and glMap2 reference pages.

query can assume
the following values:

GL_COEFF

v returns the control points for the evaluator
function. One-dimensional evaluators return $order$ control points, and two-dimensional
evaluators return $uorder ~times~ vorder$ control points. Each control point
consists of one, two, three, or four integer, single-precision floating-point,
or double-precision floating-point values, depending on the type of the evaluator.
The GL returns two-dimensional control points in row-major order, incrementing
the $uorder$ index quickly and the $vorder$ index after each row. Integer
values, when requested, are computed by rounding the internal floating-point
values to the nearest integer values.

GL_ORDER

v returns the order of the
evaluator function. One-dimensional evaluators return a single value, $order$.
The initial value is 1. Two-dimensional evaluators return two values, $uorder$
and $vorder$. The initial value is 1,1.

GL_DOMAIN

v returns the linear $u$
and $v$ mapping parameters. One-dimensional evaluators return two values,
$u1$ and $u2$, as specified by glMap1. Two-dimensional evaluators return
four values ($u1$, $u2$, $v1$, and $v2$) as specified by glMap2. Integer
values, when requested, are computed by rounding the internal floating-point
values to the nearest integer values.